As is known, tires for two-wheeled vehicles have been manufactured for a long time with a carcass structure comprising a couple of plies of rubberized fabric reinforced with cords symmetrically inclined with respect to the tire equatorial plane, which structure is usually known as cross-plies carcass, and possibly a belt structure also comprising couples of strips of rubberized fabric provided with cords inclined with respect to the tire equatorial plane.
While such tire structure could ensure an extremely regular curve holding of the motor-vehicle, the use of this type of tires involved problems of comfort, stability, road holding of the vehicle and weariness of the driver, due to their excessive stiffness.
The structure of these tires , in fact, accumulated--under the effect of an imposed deformation--elastic energy which was given back almost instantaneously upon termination of the stress, amplifing the unevennesses transmitted by the road surface layer, with ensuing stability loss of the vehicle.
To try to obviate these problems, the use of radial carcass tires with a belt structure of textile or metal cords has been recently introduced: in particular, the rear tire is provided with a belt structure comprising, sometimes exclusively, a winding of circumferentially-oriented cords, preferably metal cords, also indicated by the term: zero-degree cords.
This belt structure of the tires has unquestionably improved the situation in terms of comfort and driving stability: since the rear tire has a remarkable dampening effect, in fact, the vehicle oscillations at straightaway high speeds have in practice disappeared.
However, regardless of which belt structure type is adopted for the tires, no adequate solution has been found so far in connection with the problem of an extremely irregular and dishomogeneous wear of the edges of the grooves defining the rubber blocks formed in the tire tread, often associated with removal of bulk portions of rubber referred to in the art by the term: "chunking".
The causes of such phenomenon, particularly marked in case of tires to be mounted on the rear wheel of a motor-vehicle, are in general ascribed both to the rubbing effect of the groove edges with the road, and to the excessive mobility of the rubber blocks positioned upstream of the inlet edges of the grooves towards the rolling direction of the tire.
In this regard, it has been found that such excessive mobility causes a local overheating of the rubber composition of the tire tread, due to a high energy dissipation by hysteresis, which overheating causes in its turn a degradation of the rubber composition, facilitating the aforesaid chunking phenomenon.